The present invention generally relates to metal casting and, more particularly, to controlling the composition of a molten metal bath to provide consistency of the molten metal for casting.
In the process of making iron, steel scrap and/or cast iron are melted in a cupola and transferred to an induction furnace to provide a molten metal bath. The molten metal within the induction furnace is generally emptied into a transfer ladle which, in turn, is utilized to fill the mold to produce castings.
To produce a molten metal bath having selected percentages of desired elements, such as carbon, silicon or the like, an adjustment of the element levels in the bath is generally required. The adjustment of the element levels is carried out by the addition of elements, such as carbon, silicon or the like, into the bath to produce a molten metallic bath having the desired level or percentage of such elements. The consistency of the chemistry of the molten metal bath is directly related to the uniformity of the castings. As the level of consistency increases, so does the uniformity of the castings.
The quest for consistency is hampered generally by erratic melting of the scrap, due in part to the unknown chemistry of the scrap, erratic alloying practices and the difficulty of adding various elements uniformly over a period of time into the molten bath. Inconsistencies in the molten bath chemistry hampers the production of different grades of metal required in the marketplace.
Due to the size of the induction or holding furnace, it has the capability of maintaining a desired temperature and storing large quantities of molten metal. The large quantities of molten metal cause high and low peaks or concentrations of elements that result from their different melting rates, to be less pronounced. Thus, a more uniform makeup of the metal to be poured may be procured from the induction furnace.
In the past, the required addition of elements into the transfer ladle or induction furnace usually took the form of throwing a shovel or scoop full of an alloy or the like into the molten bath. Thus, an unknown and unprecise amount of alloy or the like was thrown into the transfer ladle or induction furnace in an attempt to provide the desired percentage of elements. Also, alloy additions have been made by gravity feed into a trough between the cupola and the holding furnace. Further, the alloy may be pneumatically injected into the bath in the induction furnace. These methods have generally resulted in erratic and generally poor recoveries.
However, the prior known methods of adding elements into the molten bath generally produce erratic results based on the inaccurate additions. These prior known methods are manpower intensive, expensive and generally produce poor recoveries (e.g. the number of satisfactory castings compared to the total number of castings cast). Other methods for adding elements into molten baths are illustrated in the following U.S. patents: U.S. Pat. No. 4,613,113, issued Sept. 23, 1986 to Saito et al; U.S. Pat. No. 4,581,068, issued Apr. 8, 1986 to Schramm; U.S. Pat. No. 4,525,211, issued June 25, 1985 to Pochmarski et al; U.S. Pat. No. 4,519,587, issued May 28, 1985 to Peckels et al; U.S. Pat. No. 4,518,422, issued May 21, 1985 to Metz; U.S. Pat. No. 4,517,019, issued May 14, 1985 to Taniguchi; U.S. Pat. No. 4,484,731, issued Nov. 27, 1984 to Taniguchi; U.S. Pat. No. 4,414,025, issued Nov. 8, 1983 to Yang; U.S. Pat. No. 4,405,363, issued Sept. 20, 1983 to Tivelius; U.S. Pat. No. 4,398,946, issued Aug. 16, 1983 to Doliwa; U.S. Pat. No. 4,352,605, issued Oct. 5, 1982 to Godding et al; U.S. Pat. No. 4,341,553, issued July 27, 1982 to Immekus; U.S. Pat. No. 4,298,377, issued Nov. 3, 1981 to Szekely; U.S. Pat. No. 4,298,192, issued Nov. 3, 1981 to Barbakadze et al; U.S. Pat. No. 4,286,774, issued Sept. 1, 1981 to Benatar; U.S. Pat. No. 4,277,279, issued July 7, 1981 to Kerlin et al; U.S. Pat. No. 4,264,059, issued Apr. 28, 1981 to Benatar; U.S. Pat. No. 4,180,396, issued Dec. 25, 1979 to Caspers; U.S. Pat. No. 4,180,051, issued Dec. 25, 1979 to Maier et al; and U.S. Pat. No. 4,052,041, issued Oct. 4, 1977 to VonStroh, III.
Improvements have also been made in the field relating to methods of obtaining chemical analysis, thus providing the typical foundry with faster and more accurate chemical analysis. A thermal arrest type of analysis, where temperature plateaus of a cooling sample indicate the levels of various elements within the sample, is used to provide quick and accurate information regarding the carbon equivalent and carbon and silicon content in the bath. This analysis can be performed in close proximity to the melting area thus providing the foundryman with a method of quickly and accurately determining the constituent levels in the molten bath. Although this method is not as complete or as accurate as a spectrometer form of analysis, it is adequate to provide the desired information. These tools enable foundrymen to determine what element additions are necessary to provide the desired chemical makeup in the final metal casting product.
The present invention thus provides the art with a method of accurately controlling the makeup of a molten metal bath thereby enabling a more consistent casting product to be produced. The present invention provides the art with an automated process of adding accurate amounts of elements into the molten bath thereby providing increased control over the elements added, which, in turn provides smaller tolerances or deviations in the makeup of the final casting products.
From the subsequent detailed description, taken in conjunction with the accompanied drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.